1. Field of the Invention
The present invention relates to a lubricating oil for a hybrid vehicle and in particular to a lubricating structure for a hybrid vehicle that can run by an engine or a motor.
2. Description of the Related Art
For example, there has been disclosed a hybrid vehicle which is adapted to run by a driving motor disposed on an axle side of a transmission (JP-A-10-324177). In a hybrid vehicle of this type, there is provided a secondary oil pressure driving source in addition to a primary oil pressure supply source for driving the transmission when the engine is driven, and this secondary oil pressure driving source is selectively used in place of the primary oil pressure supply source when the engine is re-started from a state in which the engine is stopped.
Describing the related art hybrid vehicle with reference to FIG. 3, reference numeral 51 denotes a manual valve, which is a type of manual valve which is connected to a forward clutch 52 and a reverse clutch 53. Additionally, the manual valve 51 is connected via a check valve 54 to a primary oil pressure supply source X (not shown) which is driven by an engine, and a secondary oil pressure supply source Y is connected to a downstream side of the check valve 54 for supplying a hydraulic fluid to the manual valve 51 instead of the primary oil pressure supply source when the engine is stopped.
The secondary oil pressure supply source Y is intended to supply a hydraulic fluid to the manual valve 51 from a pump 56 which operates on a motor 55, and connected to a downstream side of the pump 56 along an oil pressure path are a relief valve 57 and a check valve 58. This relief valve 57 functions to set constant the pressure of a hydraulic fluid supplied from the pump 56, and a drain for the relief valve 57 is adapted to return to an oil pan 59.
However, with the above related art, when the driving motor is run at a high output or when the vehicle is run at high speed on continuous downward slopes with the stopped engine, since lubricating system oil is not sufficiently supplied from the primary oil pressure supply X, there occurs a shortage of lubricating oil at the transmission and the driving motor, probably leading to a drawback of the failure of the devices suffering from the oil shortage. In other words, with the secondary oil pressure supply source Y which is inferior to the primary oil pressure supply source X in the provision of a needed flow rate, when an excess lubricating oil from the secondary oil pressure supply source Y is returned from the relief valve 57 to the oil pan 59, there occurs a shortage of lubricating oil that is to be supplied to the lubricating system.
To cope with this problem, an object of the invention is to provide a lubricating structure for a hybrid vehicle which can eliminate a shortage of lubricating oil while the secondary oil pressure supply source Y is in use.
With a view to solving the above problem, according to an aspect of the invention, in a hybrid vehicle comprising a transmission (for example, a CVT 6 in an embodiment of the invention) provided along a power train path between an engine (for example, an engine E in the embodiment) and a drive wheel (for example, a drive wheel W in the embodiment) which operates on oil pressure from an oil pressure supply source (for example, oil pumps 4, 25 in the embodiment) and a clutch (for example, a start clutch 15 in the embodiment) provided on a drive wheel side of the transmission, wherein the drive wheel can be driven by an electric motor (for example, a secondary motor generator M2 in the embodiment) in the event that the power train path is interrupted by the clutch, there is provided a lubricating structure for a hybrid vehicle characterized in that the oil pressure supply source is constituted by a primary oil pressure supply source (for example, mainly the oil pump 4 in the embodiment) adapted to be driven by the engine and a secondary oil pressure supply source (for example, mainly the oil pump 25 in the embodiment) adapted to be driven by any other drive source (for example, a motor 26 in the embodiment) than the engine, that a relief valve (for example, a relief valve 28 in the embodiment) is provided on the secondary oil pressure supply source for regulating a discharge pressure, and that a drain circuit (for example, a drain circuit 29 in the embodiment) of the relief valve is connected to a lubricating oil path (for example, a lubricating piping 22c) for the transmission and the electric motor.
According to the lubricating structure, an excess oil from the drain circuit of the secondary oil pressure supply source is supplied to lubricate the transmission and the electric motor.